Ngozi (Tanzania)

Ngozi caldera is the most prominent volcanic feature of the Poroto Ridge, a transverse structure at the northern end of the Karonga basin. The trachytic-to-phonolitic volcano contains a 3-km-wide caldera with a 1.5 x 2.5 km lake in the southern part of the caldera that is bounded by steep-walled cliffs 150-300 m high. Numerous pyroclastic cones are situated along the ridge. Eruption of the Kitulo Pumice, radiocarbon dated at about 10,200 cal. years before present, is though to be related to formation of the caldera. The youngest activity appears to have originated from the caldera and from youthful-looking pyroclastic cones to the north; the youngest known eruption produced a pyroclastic flow that swept at least 10 km S about 500 years ago.

Lake-filled Ngozi caldera is seen here from its southern rim. The 1.5 x 2.5 km caldera lake is bounded by steep-walled cliffs 150-300 m high. The trachytic-to-phonolitic caldera is the most prominent volcanic feature of the Poroto Ridge, a transverse structure at the northern end of the Karonga basin in SW Tanzania. Numerous pyroclastic cones are situated along the ridge. The youngest activity along the ridge appears to have originated from Ngozi caldera and from youthful-looking pyroclastic cones to the north.